The present invention relates to ultrasonic detection apparatuses to be employed such as for detecting internal defects or the like of concrete materials by means of ultrasonic waves and an ultrasonic detection method that employs the apparatus. More particularly, the present invention relates to an ultrasonic detection apparatus which provides accurate and high-speed detection of reinforcing bars arranged inside a concrete material, the depth of a crack, the thickness of concrete, gaps and the like, and to an ultrasonic detection method that employs the apparatus.
A concrete material is a composite structure of cement and coarse aggregates of 1 to 3 mm in diameter. Ultrasonic waves traveling through a concrete material are scattered while being reflected, refracted, and changed in mode repeatedly at the interface between the coarse aggregate and the cement.
This causes readily the ultrasonic waves to be diffused in the concrete material and significantly attenuated in strength in the orientation direction of the ultrasonic waves. The level of the attenuation would be acceleratingly increased as the ultrasonic waves have higher frequencies.
In addition, when longitudinal or transverse ultrasonic waves are input into a concrete material from a surface thereof, longitudinal or transverse ultrasonic waves and direct waves, each having a relatively large amount of energy, coexist with the longitudinal or transverse ultrasonic waves input to the inside of the concrete material. In addition, surface waves having a large amount of energy are generated at the surface of the concrete material.
These phenomena have conventionally made it difficult to detect the inside such as of a concrete material or a porous material by means of ultrasonic waves.
However, recent years have seen an improvement of internal detection methods employing ultrasonic waves. Thus, in some cases, with various conditions being satisfied, it is possible to measure the thickness of a concrete plate or detect gaps or the like therein within a detection depth range of about 20 to 50 cm. The conditions of the detection are shown below.
First, it is necessary to use ultrasonic wave transmitting and receiving transducers having a resonant frequency of about 100 to 500 kHz. Secondly, it is necessary to use transducers having an oscillator as large as about 50 to 70 mm in diameter. Thirdly, it is necessary to apply a stepped voltage to a ceramic oscillator or the like in the transducer instead of the pulsed voltage, which has been conventionally employed.
FIG. 68(a) is a graph showing a pulsed voltage, (b) being a graph showing the spectrum of the pulsed voltage, and (c) being a graph showing a time series waveform of the pulsed voltage. On the other hand, FIG. 69(a) is a graph showing a stepped voltage, (b) being a graph showing the spectrum of the stepped voltage, and (c) being a graph showing a time series waveform of the stepped voltage. The graphs represent pulsed and stepped voltages having values of 50 to 500V. Differences are found in the spectrum and time series waveform between the pulsed and stepped voltages. Incidentally, the peak frequencies of FIGS. 68(b) and 69(b) are resonant frequencies of oscillators, while FIGS. 68(c) and 69(c) show time series transmit ultrasonic waves.
Now, a conventional method for measuring a concrete material will be explained in which the stepped voltage shown in FIG. 69(a) is applied to the concrete material by using an ultrasonic transducer having an oscillator 56 mm in diameter whose resonant frequency is 1 MHz. FIG. 70 is a schematic view illustrating a concrete plate as a material to be detected. The concrete plate 41 as a material to be detected has a thickness of 20 cm and contains fine stones about 2 mm in diameter as coarse aggregate. In addition, the concrete plate 41 has a relatively small number of bubbles therein. Furthermore, it should be understood that this measuring method works as a method for making a measurement with one transducer, in which a transducer 42 functions as receiving and transmitting transducers. FIG. 71 is a graph illustrating a reflected wave obtained under the aforementioned conditions, with the horizontal axis representing the time and the vertical axis representing the amplitude.
Referring to FIG. 71, a peak 43a shows a longitudinal reflected wave 43 from the bottom surface of the concrete plate. The peak 43a is noticeable, showing that it is possible to measure the thickness of the concrete plate under the aforementioned conditions.
Suppose that like the concrete plate 41, the thickness is relatively thin when compared with the surface area. In this case, according to various types of measurement examples, since a corner-reflected wave 44 from a corner portion and a reflected wave of a surface wave 45 are generally small in amplitude, it is made possible to measure the thickness of a plate as thick as about down to 50 cm under the aforementioned conditions.
However, for a concrete plate having been subjected to aging, it is often difficult to confirm the generation of a reflected wave from the bottom surface thereof. Likewise, when a concrete plate is not a planar one, and great amounts of reflected waves from the corner portions and from surface waves are provided and lots of bubbles are contained in the concrete plate, it is also difficult in many cases to confirm the generation of a reflected wave from the bottom surface.
For example, the following cases make it difficult to measure thickness. FIG. 72 is a view illustrating a concrete pillar or a material to be detected, (a) being a schematic view thereof before being cut apart and (b) being a schematic view thereof after having been cut apart.
Here, such a concrete pillar 51 was made that has a side of length 30 cm and another side of length 50 cm in a cross section perpendicular to the longitudinal direction. Inside the concrete pillar 51, there is present a large number of bubbles about 1 to 10 mm in diameter. In addition, contained in the concrete pillar are 30 wt % of coarse aggregates having diameters greater than 5 mm and less than 1 cm, 40 wt % of coarse aggregates having diameters greater than 1 cm and less than 2 cm, and 40 wt % of coarse aggregates having diameters greater than 2 cm. In addition, a concrete material 51a having a height of 50 cm was cut from the concrete pillar 51.
Such a case is explained below in which a transducer 52 is placed at the center A of a plane having a width of 50 cm for measuring the thickness. FIG. 73 is a schematic view illustrating waves produced when the thickness is measured with the transducer 52 being placed at the center A.
When longitudinal ultrasonic waves are input into the concrete material 51a from a surface thereof directly downwards with the transducer 52 being placed at the center A, as shown in FIG. 73, a corner-reflected wave 54, a direct wave 55, a surface wave 56, and a longitudinal wave 57 low in strength as well as a reflected wave 53 from the bottom surface return to the center A. Accordingly, the received wave at the center A is a superimposed wave of the waves 53-57, making it difficult to determine the peak of the reflected wave from the bottom surface as shown in FIG. 71.
Various types of oscillators were actually used for the application of a stepped voltage of 500V for measurement, with the results being illustrated. FIG. 74(a) is a graph illustrating a time series waveform obtained by a measurement with a transmitting transducer having an oscillator of resonant frequency 2.5 MHz and 20 mm in diameter, (b) being a graph illustrating a time series waveform obtained by a measurement with a transmitting transducer having an oscillator of resonant frequency 500 kHz and 40 mm in diameter, and (c) being a graph illustrating a time series waveform obtained by a measurement with a transmitting transducer having an oscillator of resonant frequency 500 kHz and 70 mm in diameter. Incidentally, the receiving transducer employed an oscillator having a resonant frequency of 2.5 MHz and a diameter of 20 mm. Referring to FIGS. 74(a) through (c), ultrasonic waves are transmitted at time 104 xcexcs on the horizontal axis. For example, time 205 xcexcs in the figures shows that 101 xcexcs have elapsed after the time of transmission.
For these measurements, a two-transducer method was employed in which a transmitting transducer and a receiving transducer are arranged extremely close to each other. Referring to FIGS. 74(a) through (c), the time shown by the dashed lines indicates the theoretical time of generation of the reflected wave 53 from the bottom surface of the concrete material 51a. However, in these time series waveforms, it is impossible to identify the time as the time of generation of the reflected wave 53. Therefore, in such cases, it is impossible to measure the thickness of the concrete material 51a. 
The present invention was developed in view of such problems. It is an object of the present invention to provide an ultrasonic detection apparatus which can detect with accuracy the thickness of a concrete material having a narrow width and a thick thickness, the thickness of the covering of a reinforcing bar and the diameter thereof, the depth of a crack and the like, and a ultrasonic detection method that employs the apparatus.
A first ultrasonic detection apparatus according to the present invention is for allowing a transmitting transducer to transmit an ultrasonic wave a plurality of times to analyze an ultrasonic wave received by a receiving transducer. The ultrasonic detection apparatus comprises: an arithmetic averaging device which performs arithmetic averaging a plurality of times per one detection every time an ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves having been received until then; and extracting means which extracts an ultrasonic wave having a predetermined frequency as a center frequency from received ultrasonic waves. The abovementioned predetermined frequency is given by ((nxc2x1(xc2xd))(106xc3x97vxcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
The present invention allows the arithmetic averaging device to perform arithmetic averaging 1,000 times or more per one detection every time an ultrasonic wave is received, on the ultrasonic wave and the ultrasonic waves that have been received until then. This causes waves having variations in phase to gradually cancel out each other and only those waves having substantially no variation in phase to amplify each other to remain. Accordingly, measurements carried out under the conditions which cause substantially no change in phase of a desired wave would make it possible to detect, with high accuracy, the thickness of a concrete material narrow in width and thick in thickness or the like. Furthermore, the arithmetic averaging device performs directly the arithmetic averaging, thereby reducing the amount of processing to be performed by purpose-oriented software or the like and making it possible to perform processing at high speeds. For example, suppose that arithmetic averaging needs to be performed 10,000 times, in which the arithmetic averaging device performs arithmetic averaging up to 4,000 times and the software performs subsequent arithmetic averaging. In this case, arithmetic means obtained by performing arithmetic averaging 4,000 times, another 4,000 times, and further 2,000 times are processed by the arithmetic averaging device, and then the resulting values are processed by the software.
A second ultrasonic detection apparatus according to the present invention is for allowing a transmitting transducer to transmit an ultrasonic wave a plurality of times to analyze an ultrasonic wave received by a receiving transducer. The ultrasonic detection apparatus comprises an arithmetic averaging device which performs arithmetic averaging a plurality of times per one detection every time an ultrasonic wave obtained by applying a step function voltage to an oscillator is received, on the ultrasonic wave and ultrasonic waves having been received until then. The abovementioned predetermined frequency is given by ((nxc2x1(xc2xd))xc3x97(106xc3x97v/xcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
A third ultrasonic detection apparatus according to the present invention is for allowing a transmitting transducer to transmit an ultrasonic wave a plurality of times to analyze an ultrasonic wave received by a receiving transducer. The ultrasonic detection apparatus comprises: an arithmetic averaging device for performing arithmetic averaging a plurality of times per one detection, every time an ultrasonic wave obtained by applying a step function voltage to an oscillator is received, on the ultrasonic wave and ultrasonic waves having been received until then; and extracting means which extracts an ultrasonic wave having a predetermined frequency as a center frequency from received ultrasonic waves. The abovementioned predetermined frequency is given by ((nxc2x1(xc2xd(106xc3x97v/66 L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
A first method for detecting an ultrasonic wave according to the present invention comprises the steps of: transmitting and receiving an ultrasonic wave a plurality of times while a transmitting transducer for transmitting ultrasonic waves and a receiving transducer for receiving ultrasonic waves are moved within a predetermined region on a surface of a material being detected; performing arithmetic averaging every time the ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves having been received until then; and extracting an ultrasonic wave having a predetermined frequency as a center frequency from ultrasonic waves obtained by the arithmetic averaging. The abovementioned predetermined frequency is given by ((nxc2x1(xc2xd))xc3x97(106xc3x97v/xcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
The present invention allows ultrasonic waves to be transmitted and received a plurality of times while a transmitting transducer for transmitting an ultrasonic wave and a receiving transducer for receiving an ultrasonic wave are moved within a predetermined region on a surface of a material being detected, thereby causing a received wave having variations in phase and a received wave having no variation in phase to exist. In addition, arithmetic averaging is performed, every time an ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves that have been received until then. This makes it possible to allow received waves varied in phase to gradually vanish and only those waves not varied in phase to remain. This makes it possible to vanish unnecessary received waves to extract only desired received waves.
A second method for detecting an ultrasonic wave according to the present invention comprises the steps of: transmitting and receiving an ultrasonic wave a plurality of times while a transmitting-receiving transducer for transmitting and receiving ultrasonic waves is moved within a predetermined region on a surface of a material being detected; performing arithmetic averaging every time the ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves having been received until then; and extracting an ultrasonic wave having a predetermined frequency as a center frequency from ultrasonic waves obtained by the arithmetic averaging. The abovementioned predetermined frequency is given by ((nxc2x1({fraction (1/2)}(106xc3x97v/xcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
A third method for detecting an ultrasonic wave according to the present invention comprises the step of repeating a predetermined number of times the steps of: transmitting and receiving an ultrasonic wave a plurality of times while a transmitting transducer for transmitting ultrasonic waves and a receiving transducer for receiving ultrasonic waves, evenly spaced apart from each other, are moved within a predetermined region on a surface of a material being detected; performing arithmetic averaging every time the ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves having been received until then; and varying a distance between the abovementioned transmitting transducer and the abovementioned receiving transducer by a predetermined amount. The method further comprises the steps of; determining an arithmetic mean of ultrasonic waves obtained as results of the arithmetic averaging; and extracting an ultrasonic wave having a predetermined frequency as a center frequency from ultrasonic waves obtained by the last arithmetic averaging. The abovementioned predetermined frequency is given by ((nxc2x1(xc2xd(106xc3x97v/xcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.
A fourth method for detecting an ultrasonic wave according to the present invention comprises the step of repeating the steps of: transmitting and receiving an ultrasonic wave a plurality of times while a transmitting transducer and a receiving transducer are evenly spaced apart from each other, the transmitting transducer transmitting ultrasonic waves by receiving an electrical signal to be output from a transmitting circuit, and the receiving transducer receiving ultrasonic waves to input an electrical signal to a receiving circuit disposed in a housing different from one for the transmitting circuit; performing arithmetic averaging every time the ultrasonic wave is received, on the ultrasonic wave and ultrasonic waves having been received until then; extracting an ultrasonic wave having a predetermined frequency as a center frequency from ultrasonic waves obtained by the arithmetic averaging; and moving the transmitting transducer and the receiving transducer on a surface of a material being detected. The abovementioned predetermined frequency is given by ((nxc2x1({fraction (1/2)}))xc3x97(106xc3x97v/xcex94L))(Hz), where xcex94L is a variation in distance between the abovementioned transmitting transducer and the abovementioned receiving transducer, v is a transmission velocity of an ultrasonic wave transmitting in a material being detected, and n is a natural number.